An undo technique with improved ease-of-use is provided. An undo manager displays an undo UI screen in a lower portion of a screen displayed by a document processing apparatus. A time axis is displayed on the undo UI screen. Furthermore, an operation history is displayed along the time axis. A slider is displayed on the time axis. Upon a user moving the slider in the horizontal direction via a mouse, the operation process is displayed on the screen according to the slider operation in a manner like that of the playback of a moving image.